Speciation of sulphur in asphaltenes and resins from Argentinian petroleum by using XANES spectroscopy

Argentinian crude oil samples from different origins have been processed to separate in the four fractions Saturates, Aromatics, Resins, and Asphaltenes (SARA). Asphaltene and resin fractions were extracted using n-pentane and n-heptane as precipitating solvents. Sulphur contents of the samples were determined by elemental analysis and X-ray Absorption Spectroscopy at the Sulphur K-edge was used to perform sulphur speciation for resin and asphaltene fractions. Reduce sulphur as sulphides, disulphides and thiophenes dominate the spectra of asphaltenes, resins I and crude oils samples. A higher abundance of sulfoxide forms were found in the resin II fraction. In addition, it was found that the asphaltenes are more enriched in aromatic sulphur (thiophene) when the n-heptane solvent is employed. From the sulphur speciation determination it was possible to incorporate different sulphur forms in the hypothetical average molecular structures for the Argentinian asphaltenes.